https://docs.magento.com/m2/ce/user_guide/cms/editor-insert-link.html

Inserting a Link

An easy way to insert a link is to use the Link button in the editor toolbar. It doesn’t require any knowledge of HTML, and the result is the same.

To insert a link:

1. Highlight the text where you want to create the link. Then, in the editor toolbar, tap the Link button.
Insert Link Button
Insert Link Button
2. In the Link URL field, enter one of the following:
  • The URL Key of a page in your store.
  • The full URL of an external page to be linked.
3. Set Target to one of the following:
  • Open link in the same window
  • Open in a new window
4. In the Title field, enter the tooltip text to appear when someone hovers over the link.
5. Tap Insert to create the link.